For many injection devices intended for self-administration of medicament, it is often desirable that the device is as complete as possible, i.e. that the number of operations or assembly steps needed in order to make the device ready to deliver a dose of medicament is minimized.
One solution for keeping a medicament delivery device as pre-assembled as possible is to deliver the medicament delivery device with a delivery member, such as a needle, pre-attached. This solution often causes the rear end of the needle to protrude into the interior of the container, which could be a drawback if the medicament reacts with the material of the delivery member when exposed for a period of time. In that respect it would be desirable to have the rear part of the delivery member outside the container until the delivery is to be performed.
On the other hand, the front part of the delivery member has to be protected before use in order to prevent unintentional needle sticks and in order to keep the needle clean. The front end of the delivery member is therefore often arranged with a sheath and/or a cap that has to be removed beforehand.
In order to accomplish the above in a simple and effective way, the applicant has developed a cap assembly that comprises a retainer member connectable to a medicament container holder of a medicament delivery device. The cap assembly further comprises a hub coaxially movable within the retainer member where the hub comprises a needle having a proximal end and a distal end. An inner cap is interactively connected to the hub and the retainer member. The engagement between the outer cap and the inner cap and between the inner cap and the retainer member is configured such that removal of the outer cap causes the hub to move distally such that the distal end of the needle penetrates the proximal end of the medicament container.
The cap assembly also comprises a safety feature comprising an outer cap clutch provided between the outer cap and the housing of the medicament delivery device where the clutch is set in engagement when the outer cap is actively moved towards the housing. The outer cap clutch is further arranged to prevent the user from applying an excessive force in the wrong direction when removing the outer cap from the cap assembly. Thus, the cap clutch ensures that the outer cap is not accidentally removed without the active safety operation, and that it is correctly removed in the right rotational direction.
The above design has proven to work well in most cases. However, it has been noticed that if the device is subjected to sudden external forces, such as a drop of the device onto a surface or vibrations during transport, to mention a few, then the cap clutch may be moved such that it becomes engaged even without the active movement of the outer cap in relation to the housing. This may in turn enable removal of the outer cap without the safety operation of moving the outer cap towards the housing.